The present embodiments relate to wireless communication systems and, more particularly, to the CoMP or Coordinated Multi-Point Transmission.
The term CoMP stands for Coordinated Multi-Point Transmission. In CoMP multiple transmission points such as macro evolved Node B (eNB), pico eNB, femto eNB, remote radio heads (RRHs), distributed antennas, other wireless transmission entity or combinations coordinate with each other to jointly optimize downlink transmission signals to user equipment (UE). This cooperation includes beamforming vectors, transmission power and/or scheduling decisions. In traditional wireless networks signals from other transmission points are regarded as co-channel interference. In CoMP coordination between multiple transmission points allows the signals to be cooperatively designed to reduce co-channel interference, boost received Signal to Noise Ratio (SNR), improve cell-average throughput and improve cell-edge coverage.
User equipment (UE) feedback is critical for wireless network operation. Each UE measures downlink channel state information (CSI) and reports to the network for downlink scheduling. Implicit feedback is the most prevalent CSI feedback framework. The CSI report is typically in the form of a recommended transmission format, including rank indicator (RI), precoding matrix indicator (PMI) and channel quality indicator (CQI). Rank Indicator (RI) is the number of data streams (layers) for downlink transmission. Precoding matrix indicator (PMI) is the index of the recommended precoding matrix, confined within a given codebook. Channel quality indicator (CQI) is the Signal to Noise Ratio (SNR) values, supported transport block size (TBS), or supported modulation and coding scheme (MCS) that can be used for downlink transmission. In the patent application the CQI may include one or multiple CQI values corresponding to different spatial layers.
Single-cell feedback is the baseline for most existing wireless network standards including LTE Rel. 8/9/10. In the prior art CSI is only measured and reported for the serving cell of a UE from which it receives downlink data. For the serving cell a single RI value is reported for the entire system bandwidth (wideband RI), a single PMI and CQI can be reported for each subband (a continuous frequency spectrum in the system bandwidth). The reported PMI/CQI corresponds to the reported RI value.